That will only work if you jack the trailer up by the frame, not the axel.
Yes, you're right.
The following is not directed at you, just general info for all to consider...
I'm not a fan of jacking on the axle, I much prefer to use the frame.
While many do jack on the axle, it can be a risky thing.
You're compressing the spring, which can have a nasty side effect if the axle slips off the jack...
The other danger, is that while most folks would have the trailer safely coupled to the tow vehicle while changing a tire, some may not.
When you jack under the axle, you are lifting at or ahead of the balance point.
Whenever lifting a trailer, you should have three points touching the ground at all times
The normal points on a tear or single axle trailer are; the two wheels, and the tongue jack.
When you jack up one side, the jack replaces the wheel (as one of the three points).
When you jack at or ahead of the balance point, the wheel and tongue support come off the ground...leaving only two points.
At this stage, the slightest nudge or sneeze can cause the trailer to pivot.
If you're lucky, it will pivot away from you, if not...
Each year, people die because they were jacking up a trailer, and it crushed them...all it takes to prevent this is three points...