No. The CRT is perfectly linear. It is off-set at an angle to the top of the unit. If you take a look at the eBay listing you will see the instrument in its entirety and then all should become clear.
I agree with your comment about the technological advances. The Tester 301A had a CRT; the Tester 301C has a TFT display.
Ah yes, I hadn't looked at the original listing and it's photos.
There's something broadly historic about that particular shade of metallic green!
[As an aside, today while driving, I passed what resembled a Morris Traveller Van, in BT/GPO Yellow, immaculate condition, with a ladder on top and "GPO" on it's side. On the rear was a Buzby advert sticker]
Ian