They alluded to it, showing the vats of snoke-esque body parts, as well as the classic “unnatural” line, but they never outright explain it. Basically, unless you’re a hardcore fan who can pick up on the hints, I think you’d have a hard time understanding how he came back. Hence the criticism of the “Somehow” statement. Personally, I just think it is a bad line. It highlights that if the writers really wanted to bring Palpatine back, they would have needed to build up to it throughout the trilogy. By just saying “somehow”, the skip over what could have been a captivating mystery, had they had the time to make it. That, in my opinion, is the biggest flaw of the sequels. The lack of direction with no ending in mind. In my opinion, a good plot twist has clues that build up to the big reveal. That is mostly nonexistent here, as it’s clear Abrams vision in mind when making The Force Awakens. He just wanted to say he made a star wars movie, then move on with his career.