No you don't have to strafe jump there.
I suspect you've done some cheating...
Here is the build pic. As you can see there is a sectoreffector to the right in the corner who raises another "step" just outside the entrance. 
I didn't cheat. If I did, it was because I might have found an exploit without realizing it. I got into that big room, killed everything, wandered around until I noticed some machine noise next to a wall, seen that it was textured darker than the rest of the wall, jumped up to the room behind the masked wall, triggered the alien button, killed the newbeast, the other switch next to the (I assume) fake door didn't do anything like it was untagged, went back into the big room and seen the pillars, the last pillar was only a couple clicks up from the floor, strafe jumped up to where the underwater passage is off the second to the last pillar.
BTW, check the code. I killed the overlord at the end of the map, it played an episode ending "movie" clip as it would when a boss is killed, then the game exited to the main menu instead of the next level.
I'm playing 32 bit, no mod, no hrp