Being familiar with the plastication process, I can say with 100% certainty that this came out of the box. With these being bent, 1 of 2 things occurred.
1) The mixture during the fill process was off, causing issues during the cooling process. This causes integrity issues like thin zones, brittle areas etc. The casing seems to be fine, however, so outside of a few cases I do not think this would be the case.
2) The cooling process itself. If the manufacturer hastens the cooling process, and does not allow for the casing to set before ejection, the productiwill most likely warp. During my time in the plastication industry there were Q&A tests for these type of things. So I'm guessing these meet the manufactures, and Nintendo's, specifications for retail.
EDIT: To add, I'm sure the Switch casing was given a hardener during the fill process. So while it probably takes around 700 degrees initially to melt, it will take much more than that to break down once bonded together after cooling. Likely scenario is that the case would burn (wouldn't melt) due to the additive. I highly doubt the Switch get's that hot. So the dock some how molding it as the player is playing is very highly unlikely. I would go as far as to say impossible. 100% straight out of the box. If the plastic was that pliable while warm, I'm sure there would be finger indention's in the back of the Switch.