Definitely try 29.625 next time and see if they get back to you. Chances are they aren't even aware they're operating in 10 meters. Some people would encourage you to try and chase them down below 28.000 MHz (or, in this case, maybe easier to chase them above 29.700 MHz??) but that can often have mixed results...
On a 10 band radio covering 25.615-30.105 MHz, with 25.615-26.055 MHz being the de facto standard "Band A" and the legal CB band being "Band D" (0.450 MHz per band), 29.625 MHz is Channel 37 on "Band I". I have a feeling these guys were using the real CB channel 37 and decided they wanted a clear or "private" channel so they just flipped the band switch up several bands.
I also imagine their antennas aren't very resonant 2+ MHz away from the center of the CB band...so if the signals are strong they're likely quite close to you and/or are running considerable power. Probably a combination of the two considering how far away they are from where their antennas are likely tuned for. Since most CB antennas are cut "long" (out of the box resonate lower in frequency), and a lot of people never actually bother to tune their antenna, you could be hearing people potentially stressing their finals pretty well too.
The real question is, how do you condense that into "flip that band switch down 3 or 4 bands and your radio will last a lot longer and perform better" and would the truckers/logging operators in question actually care? I'm sure there are dozens of clear frequencies below 28.000 MHz too...usually when I hear truckers operating out of band, they're using frequencies
below CB channel 1, the most popular ones being the channel 19 of each respective "band" on their radio. So that's 25.835 MHz, 26.285 MHz, 26.735 MHz (extremely popular), and 27.635 MHz. Going "up two bands" from CB channel 19 puts you on 28.085 MHz (yes, I've heard lots of truckers on that frequency as well).
Another popular thing to do is for truckers to have a "company channel" and use that (instead of channel 19) as the starting point. It's possible that channel 37 is the logging/trucking company in question's "company channel" and that's why you're hearing these folks on that particular frequency. It's a lot easier to ask the person you're talking to go up or down a certain number of bands than it is to ask them to go up or down a certain number of bands and then change channels. Assuming the people you're hearing are using different models of radios, there is the potential for folks to end up on different frequencies...so the "QSY" method is generally something like "hey, go up 3 bands" .... and the channel selector is never touched, just the band switch.
See a 25.615-30.105 band+channel frequency chart here:
https://www.bellscb.com/cb_radio_hobby/Stryker_10-band_frequency_chart.jpg
