20 months is such a confusing stage because growth spurts and the start of terrible twos can honestly look so similar. My girl went through the same thing around that age, wanting me close but pushing me away at the same time, and it turned out to be a bit of both happening together. The crying it out for 10 minutes then calming down on his own sounds like he is also starting to learn to self-regulate, which is actually a good sign lah. Just keep your routine consistent with milk timings so he is not caught off guard by hunger, and hang in there because this phase does pass.