Our LO has tensed a few times too and yesterday arched her back / turned her head once when eating solids. I have absolutely no idea what it is or if it's a normal reaction to eating food (maybe it's particular types of food?), but keeping a close eye at the moment.
Update- the doctors said it’s because he wanta to hold the spoon and feed himself and offer lots of finger foods at the same time. tried it and no more tensing up!
my little one does the same thing, not sure what it is