It's from Mewing.  It's not normal.  I don't know why you started Mewing... may I ask?  Anyway... you probably wanted to look more attractive and think... what the heck?  Why not try it, right?

you could be subconsciously chin tucking, when i chin tuck it applies a lot of pressure with very little to no effort

I don't think so. If anything, chin tucking makes it easier for me to keep my tongue up while exerting less pressure on the palate and alveolar ridges.

Since this is happening to you while walking, it could mean that your hips are at a neutral tilt and working as they should (which will mechanically guide the tongue on the palate), or that you feel tense around people.

Interesting. I've been fascinated with walking and how it relates to mewing for the past couple months (especially after helmut's transformation and his technique of walking with a chin tuck for multiple hours a day).

I believe that what you're experiencing is good, the rest of your body is in alignment and the tongue naturally tries to go where it belongs (up on the roof), and perform its role in the walking motion. However, since you likely have suboptimal bone structure like most people, two things are happening -

1. Some degree of forward head posture means that less of the posterior tongue and more of the anterior tongue making contact with the palate

2. The maxilla is down and back. This means that the maxilla is in the way of the ideal tongue position. Thus, the tongue tries to push it out of the way with great force.

You should add chin tucking to walking to get more of your tongue up on the palate, and make great effort to make the posterior tongue part of the walking circuit. If done right, the posterior tongue will apply a great deal of force onto the back of the palate and hopefully create expansion over time.