Some other probable causes to add....
Did you add any fragrance to your oils before adding the lye solution? Sometimes, depending on how ornery the FO is, an immediate trace can occur when the lye water hits the oils with the FO already in it. Whenever using a misbehaving fragrance that is notorious for doing that, one should forego the stickblender and hand-stir instead.
Another probable cause could be your lye solution %. If you are using a very concentrated lye solution like 50%, or to close to it, expect the oils to trace much quicker than normal.
The olive oil you used might have been a factor. Carebear brought up a good point when she asked if you were sure your olive oil was pure, because it turns out that some olive oils being sold and labeled as olive oil have been found to actually be spiked with a mix of other oils, which in turn has been the cause of various troubles for some soapers.
I didn't check the temperature of the lye solution, as I recently read a book by a well-known chemist that said the temperature of the lye isn't important (is he wrong?)
Well, yes and no. What I mean is that it all depends on your formula and what types/how much of solid fats you are using, and how hot the fats are when they are in their melted state. If your lye solution is cool enough so as to bring the temp of your melted solid fats down too much below their melting points, then, yes, the lye solution temp matters in such a case in that it will cause what is known as a
pseudo trace. On the face of things with a pseudo trace, it looks like the batter is coming to a thick trace pretty quick, but in actuality the solid fats are just resolidifying or precipitating out before the lye can work it's magic on them. The finished bars of pseudo-taced soap have tell-tale white spots throughout the soap (stearic spots). It's not dangerous or anything (unless the soap refuses to be tongue neutral over time, that is), but just unsightly. If you're just using mostly liquid-at-room-temp oils, then the temp of the lye solution is not a critical factor.
In my soaps with a goodly amount of hard fats such as hydrogenated PKO, cocoa butter, mango butter and/or kokum butter, I like to heat my oils/fats to 120 degreesF and have my lye solution just barely warm to the touch when I feel the outside of the lye container. This works well for me at keeping pseudo trace at bay, especially when I add my cooler, room-temp colorants and FO.
IrishLass