You better look again, or hope your DM doesn't look to closely:
Improved Grab
If a creature with this special attack hits with a melee weapon (usually a claw or bite attack), it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity. No initial touch attack is required.
Unless otherwise noted, improved grab works only against opponents at least one size category smaller than the creature...
The version of Improved Grab that
Scaled Horror gets
is "otherwise noted", and works against creatures of the
same size or smaller.