True if the OP was forcefully applying the brakes. But OP may have been only pushing on brake pedal lightly, bc they were just pulling into a parking spot, not decelerating from freeway speed so to stop at the stoplight at the end of a downhill off-ramp.
Accelerating when stepping on the brake, the car is designed and tested so as to make sure even if a part fails that doesn’t happen, and such a thing rarely does happen fortunately. But no design is perfect and I concur with the above posts, it makes sense to get the car looked at by a pro. They’ll look at the accelerator pedal and brake pedal ass’ys, the throttle’s electronic actuator and relay, at the carpets & mats, old coca cola cans rolling around, assess if something like that was involved, etc, and test/inspect the IAC (or drive by wire ass’ys) and brake booster for anything that might be wrong. My guess, the most likely explanation is the accelerator pedal was pushed by something either directly or indirectly while you were stepping on the brake pedal.
If that happened to me I’d remove all the carpets/mats from the driver’s area, give the whole interior a good clean out and vacuuming (esp under the seats), and remove anything inside the passenger compartment that wasn’t there when the car was purchased new. All the extraneous stuff ( stuff that most of us in our cars), I’d put that all in the trunk for the time being. I’d also probably drive wearing plain ordinary tennis shoes and switch to formal or better shoes when leaving the car. On a temporary basis I mean, untill the problem is eventually discovered.
Re: airbags. Hard to say whether they should have deployed or not. It is quite expensive to replace deployed airbags with new ones, so you avoided a big expense there by them not popping, if you are a “silver lining” sort of person. . If you think the airbag system may be faulty, hire a pro to perform the air bag test procedure.