If your gravel is mostly as shown in the photo, then the first mistake was riding GP 5ks and the second mistake was riding them at 100 PSI. I couldn't resist being glib, but we shall subsequently drop that.
High-performance tires vs. endurance or all-season tires
The Bontrager R1 is described as having "Hard-Case Lite puncture protection", and it's described as a reliable entry-level tire suitable for road bikes or urban commuters. The GP5000 also has a puncture protection strip under the tread. In both cases, it's probably made of something like kevlar. Otherwise, the GP5000 is a performance road tire, and it's likely to be less sturdy in construction than the R1.
In my experience, the GP5000 is perfectly fine on dirt roads without that much gravel. However, I am about 145 lbs. Heavier riders encountering a lot of sections of the pictured gravel, which is very chunky, are likely to have a worse experience. This could have contributed to the flats. The previous response didn't consider rider weight. Cyclists come in many shapes and sizes.
If you browse tire manufacturers' offerings, you should be able to see a performance road tire, a first- or second-tier endurance road tire with a tougher construction, and a time trial tire. For Continental, those are the GP 5000 S TR, the All Season (AS) TR, and then the TT TR plus the new aero tire. The AS TR is an equivalent level of technology to the S TR, but I don't think everyone does this. The Vittoria Corsa NEXT is another example. There's no industry standard term, but I'm calling this the endurance road tire.
At a given level of technology, you can optimize the tread compound for a combination of rolling resistance, grip, and durability. The high-performance all-round tires (e.g. the 5000 S TR) are going to lean more towards rolling resistance and grip. The endurance road tires like the AS TR are likely to downplay rolling resistance for durability and grip.
If you are doing a lot of off-road excursions, the AS TR is a better choice. It's a couple watts higher rolling resistance per tire at high speed. However, it's overall a sturdier construction (which increases hysteresis losses while the tire is rolling, therefore increasing rolling resistance). That isn't to say that the S TR cannot be used on dirt roads. It certainly can, it's just not ideal.
In addition, you might consider going tubeless if you bought the tubeless versions of those tires. With a 32mm tire, it's likely that you will see at least some benefit from the sealant, although my intuition is that if you run very high pressures, that may be diminished.
Some companies have a durable tire, like the Continental Gatorskin and the Pirelli Cinturato Velo. The Gatorskin definitely has very high rolling resistance and may be uncomfortable to ride. I feel like that's not necessary for this application.
Pressure - Even 70 PSI is almost certainly too muchg
Try the Silca tire pressure calculator here. For 32mm measured width on chunky-ish gravel, it suggests 47 PSI front/48.5 rear. I don't know if excess pressure contributed to flats, but it definitely can't be comfortable and is actually slower. For that matter, the Silca calculator is calibrated to minimize rolling resistance, and it is biased high relative to some other calculators. For 28mm road tires, I run 5-10 PSI less than my suggested pressure.
Also note that you can click the surface guide link in that calculator for examples of what they consider each surface type, as pressure recommendations vary a bit by surface. Here's the direct link. I assumed category 3 gravel. For category 2, which is a hard packed dirt road with a bit of gravel, it's suggesting 53/54.5 PSI. For new pavement it's suggesting in the mid 60s. It's suggesting over 70 PSI for tracks, although a road bike with 32mm tires would be a bit of an unusual choice for track cycling.
