pg 50, every weapon has a profile. here are two examples.
gun
sword
then they list ranged weapons, melee weapons, grenades and read the bold under these headings.
just grenades, not grenade weapons and no mention of weapons in the bolded description. This is what I mainly base my conclusion on.
yet under vehicles and mostrous creatures, a model can use such a grenade as a melee weapon
it's used as a weapon, because it's not a weapon.
And some unusual grenades do not have a profile, ie not a weapon.
grenades and shooting "throw a grenade, rather than using another shooting weapon"
which does seem to equate throwing grenades to shooting weapons
to me it seems overall that grenades are not "weapons", but it really can go either way. Maybe it will be more clear in june