This is right, though I think we should be clear that the MBSs lost value because they are normally like bonds, and bond prices decrease when yields increase.

MBSs tend to remind people of '08 when MBSs lost value because too many had a bunch of garbage loans which defaulted, causing MBSs' face values to decrease. In this case, the fact that they were MBSs is mostly a coincidence. If SVB had invested in Treasuries, they'd be in the same world of hurt that they're in today.