Noone likely noticed for a couple of reasons.
1) If you spend little time on the same instrument and set-up you have little time to develop or instill a sense of "normal" sound on the new pieces. So it may be difficult for people (especially those not paying attention) to notice, since they have no basis of comparison
2) Noone was paying attention
3) Many tuba's DO sound different, but it isn't necessarily the key of the instrument that does it. In our lessons studio, we took a day to listen to multiple recorded performances by profiled players soloing (one piece was the Hindemith Sonata). The key of the tuba's varied in the recordings. Some being on CC others F and Eb...and even one I heard on Bb. The F horn....VERY distinguishible. The Eb and CC were sometimes similar, but since we were paying VERY close attention we could identify which were wich.
BASICALLY, Different key'd horns still have a certain sound, and MOSTLY particular characteristic on certain notes. The fact that there was usually a larger horn playing (CC on #1 and Eb on #2) can also "mask" up the Eb sound.
Now, your director may not have "noticed" because the sound he was still hearing was Tuba. And it sounds as if notes wern't an issue and etc. Essentially, it is a tuba players goal to sound as much like a Tuba on ANY key'd instrument you can.
The fact also, is that you were playing in a Wind Band where Bb and even Eb are acceptable. And it also has to do with the literature you played. If you were both on Eb's for something that needed more *umph* and breadth, then the director may have noticed.
Your experiment shows a few interesting things, but maybe not what you are initially thinking or trying to get across.





