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.
With a head to head like that it looks like Inter will win this game again and I think Inter have been more consistent in the Champions League this season than in the domestic league. We know the middle of the season has been really bad for Inter to be able to get the most out of it in the domestic league and they have often suffered back-to-back defeats. But on the other hand Milan does have a pretty good record in the domestic league and I quite agree that results in the domestic league are not a definite reference for favoring Milan in the Champions League semifinal match. We know very well that the Inter champion league mode is far more dangerous for its opponents.