Still not silly.
What's silly is your presuming that I'm trained to play in fifths.
You are taking this more seriously than I intended and I did not presume that you were trained in fifths, I presumed that the cello owner was. Most of the time that would be a valid assumption. Cellos are tuned in fifths for many reasons, one of them is that their construction resonates better with that tuning. The double bass players who switch to fifths find this out to be true as well on their instruments which share some of the same construction details. They almost always report that their instruments just sound better in the fifths tuning. Fifths can be a bit unwieldy and therefore takes an extra level commitment on a scale length of 34 inches, not to mention a double bass's 43 inches but already at 30 inches it is noticeably easier to do some things and at the 27 inch scale length of a full size cello it is quite comfortable. So, sorry if I offended you by using the word "silly" but seriously, you are missing a lot if you tune a cello in fourths. Rather than tuning it to the standard guitar's EADG, leave it in its standard CGDA tuning which goes both lower and higher and now see how much your musical horizons expand!