Yeah most likely, there are many factors that determine the club is favorite or underdog, head to head are one of the factor. But San Siro is the AC Milan's home, if Inter Milan play, the stadium is named Giuseppe Meazza.
I still don't agree AC Milan will able to beat Inter Milan, Inter Milan is well rounded club while AC Milan only relying Leao and Giroud. Giroud is currently injured, so that's might the behind reason why AC Milan is underdog in this match. But Giroud is expected able to play in early May, maybe the odds will be changed when the date already closer with the match.
Inter milan has dominated the match against ac milan in the last 5 meetings between the two, where inter milan was able to end 3 matches with a win and 1 defeat and 1 draw which made the bookies give odds for inter milan as the winner in match.
So, if you see that opportunity, I think the bookies has given the right oods in the meeting between the two in the Champions League semifinals. but in their performance in Serie A, Inter Milan is lagging behind AC Milan in the standings table, but that is not a strong reference if AC Milan is better than them.