It's not just their mass and general size. Moose have very long legs so, in a collision, a lot of the front car parts designed to absorb energy can end up largely passing under the bulk of the moose and upper structure offers relatively little protection.
The grandparent comment says "be bit by a moose", so that's a slightly different scenario. Of course if it's biting out of fear or aggression, it's also likely to knock you down and stomp on you, and you probably wouldn't rather have that. It's not rare for moose to kill people that way.
As for collisions, the highway the author was driving on has a speed limit of 55 or 65 MPH in most areas, and people often treat speed limits as suggestions. I had a near miss with a moose on the same highway, after which I would suggest taking the speed limit seriously.
I'd much rather be bit by a møøse than hit a møøse.