It was a wonder for Matt Ryan to be there at all. Inside TD Garden. Next to his Celtics teammates. The team plays 200 miles away from the Yonkers, N.Y., cemetery where he worked a year ago. After attending three colleges in a five-year span, averaging 7.9 points per game across his stops, he is now approaching a most unlikely championship ring. Though his contract status will not allow him to appear in games, Ryan has plenty of reasons to be the happiest guy in Boston, just like he typically appears to be. The first year of his professional basketball career, once on pause before it could even begin, has carried him from the grave to the NBA Finals. “I haven’t heard a story like that, like mine,” said Ryan. “It blows my mind. I can’t even believe this is my story, but it is.”