To some extent, you can use online physical activity compendiums to double check the calorie values. They express the typical effort for various exercises in METs, which means metabolic equivalent of task. As discussed here, the oxygen we burn is the amount of energy our bodies consume. Researchers have used labs to measure the oxygen/energy consumed by various representative activities. METs are normalized to body weight. Our resting metabolic rate is often assumed to be 1 MET, but this is a slight overestimate, typically.
Anyway, METs can be converted to calories. 1 MET is defined as 3.5 mL oxygen per kilogram per minute. Alternatively, that's equivalent to 1.162 watts per kg body weight. You can convert that to calories.
Walking has been estimated to cost 2.5 to 3.5 METs for casual speeds on flattish ground. Faster paces are higher. Let's assume you spent 1h 20min at a slow pace. With a body weight of 108 kg, I get:
2.5 - 3.5 METs * 1.162 = 2.905 to 4.067 W/kg
At 108 kg, that's 314 to 439W consumed
For 4800s, that's 1,507 to 2,107 kJ
1 kJ = 0.239 calories, so that is 360 to 504 calories
Those figures are very much a ballpark. They do suggest that the Strava estimate may be a bit high. Without meaning offense, I assumed you were working at the lower end of the range of walking intensity, given that you were exercising for 1h 20min. It does depend on how fast you hiked and what terrain.
If you check the physical activity compendium for cycling, you can see a similar range of figures, starting a bit higher than walking. Moderate exercise (by the usual definitions in the published health literature) is defined as 3 to 6 METs, and walking and leisurely cycling can fall in that range. My hunch is that easy cycling probably starts at more like 4 METs, as it's hard to keep the bike stable if you are moving really slowly. You reported that the bike ride felt tough. So, you could have been burning more like 5-6 METs.
You can plug the numbers in yourself, but that may imply close to double the calories from the walk (given that the time spent is very similar). As a check, on slow and steady rides, I typically burn 400-500 calories per hour estimated with a different method (cycling power meter, assume that there's at least a 10% error in that measurement). I am lighter, but more experienced as a cyclist. So, 300-500 calories for about 1.5 hours sounds possible.
Because cycling is low impact, it's possible to exercise harder and/or longer than walking. That said, at some point, some impact exercise or weight training is generally recommended for good bone health. Also, everyone starts slow, the point is to keep doing it. If you get experienced enough, you are likely to be able to do over 6 METs for an extended period of time. Even if not, it is still good exercise and has mental benefits as well.
For overweight people, the stated MET costs in the compendium may understate the actual energy consumption. Reasons are explained here. It also gives a formula for a better estimate of your resting metabolic rate (remember, this is wrongly assumed to be 1 MET) accounting for sex, height, weight, and age (see the Harris-Benedict equations in the link), and from there, you can correct your estimated energy expenditure for whatever physical activity. I didn't perform those corrections because this is all very rough science; the OP's actual MET costs are unknown. That said, if they were willing, they could strap something like the VO2 Master over their face and go exercise - but that thing costs something like US$8,000 and you have to wear it the whole time you're exercising.
4'250 Cal/100km, which is equivalent to about 470g fat, or about0.51 l/100kmbiofuel (cooking oil). How far can you drive your car with half a liter?