Opening up wrong Sefer Torah (Chol HaMoed Pesach)

Question

In Eretz Yisrael on the first day of Chol HaMoed (just mentioning this to say where it happened) 2 Sifrei Torah were taken out for Krias HaTorah. They put one Sefer down on the bima and the other was held by someone on a bench behind the bima. They opened up the Sefer Torah and realized it was the one that should be read from 2nd, not first. They asked someone there who is a Rov what to do and he said to roll this one to the right place and read from it instead of bringing up the 2nd one that was already rolled to the right place.

What is the source for this? If both Sifrei Torah were already taken out why can't the one on the bima be switched with the one on the bentch? Seemingly if we already have a Sefer Torah out of the Aron Kodesh that is ready to be read from better perhaps then "bothering" the tzibbur by rolling the Sefer Torah to the proper place. As well perhaps this is not going to be a problem of thinking there is a pagum in the Sefer Torah when they are already both out.

Update: While I don't think this would be done practically. However in such a case why can't first the reading of what is really the "2nd" Sefer Torah be done before the normal reading of the day (which is in the first Sefer Torah.)

Answer 1

Seemingly the Rov was wrong in his psak.

In OC Siman 684 Sif 3 we find that on Rosh Chodesh Teves (when it's also Channukah) we take out 2 Sifrei Torah and read first the kriah from Rosh Chodesh and then the kriah from Channukah. The Rema says that if one makes a mistake and reads Channukah first that they must be mafsik and read the kriah of Rosh Chodesh. The M"B however brings from the Taz that if one started Channukah first (by the aliyah of Cohen) they should finish the aliyah of the Cohen with the kriah of Channukah. Although there are cholkim on this many achronim paskened like the Taz. The Biur Halacha there in d'h "v'im to'eh v'hischil..." says that if one started to read Channukah first they should finish the aliyah of Cohen with the kriah of Channukah like the M"B writes. He adds however that a "haschalah" (a starting/beginning) of the kriah is if the brachos were already made then one should finish the first aliyah with the Kriah of Channukah. However he says if the brachos were not yet said, even though the person was ready to begin the kriah of Channukah he should close this Sefer Torah and read in the other Sefer Torah that was taken out to read for the kriah of Rosh Chodesh. There is no reason to be choshesh he writes and says that there is no pagam in this Sefer Torah since it'll be read afterwards. Seemingly the same would be true in the case here of Chol HaMoed Pesach.

Answer 2

I believe that the reason is so as not to dishonour the first Sefer by suggesting that it might be pasul. I am fairly sure that there is a source , so if someone knows it - please add. (posted in Israel)