True, there is this risk as well. We can't really compare if our speed of technological progress is better or worse than average. We can meet aliens which would be so surprised by our technology they wouldn't close their mouths until after WE conquer THEIR home planet ... or aliens who will do mistakes hurrying here out of fear we will match their technology level before they get here.
... or, we may get aliens who are able to predict EXACTLY how fast we invent things. The first transmission we catch on the first prototype of FTL radio will start "-mly welcome the civilization of planet Earth to our communication network."
... ok, they did get it few seconds wrong.
This reminds me the novel where aliens arrived on planet just days before it's sun explosion hoping they can save someone and was surprised noone is home. They later found that despite their primitive technology, natives build fleet of slow generation spaceships and evacuated on them. The alien commander was able to find the direction they flied, easily caught up and started first contact, despite his second of command joking that they should be careful with this determined species as their galactic republic outnumber them only like twenty billions to one.
Just twenty years later, that note was no longer funny.
Let me guess. One of the non native civilizations is a group called "Men" who were apparently from a planet the Earthlings called "Mars". And the other civilization is a group called "Women" from a place called "Venus".
I was thinking actual three different spaceflight capable civilizations meeting on Earth, but your idea isn't bad either. Except the aliens would need to be very stupid or very sloppy in Venus observation to believe anyone looking remotely human lives there.