New Judge, let's look at the question again. Do you see the part- sentence "Also I think you would need to know the SG of heating oil as well"? I'm sure you're aware that SG means Specific Gravity. Therefore, your assertion that "Nothing said about Specific Gravity" is plainly incorrect as the OP does mentuion it. Yes or No?
I am grateful that you concede that there was a remote possibility that the OP required the SG in order to calculate the total mass of the tank. I'm afraid that I'm satisfied that the OP did indeed mention it somewhere along the line as you put it by raising the issue of SG in the original question, albeit a very brief mention.
I am pleased that you are prepared to admit that I may have been correct on this issue.
Turning to the issue of pedantry New Judge, science tends to be exact and precise and leaves little room for impreciseness. If you desire to consider that my correction of your sentence is pedantic, you a perfectly at liberty to do so so. However, to a scientist a litre of water is not the same as a litre of mercury. I regret I am unable to discuss the feelings of other professions regarding your sentence, which clearly are identical to those of lay persons.
As you state, your correction is not tautological and I'm grateful for you're alternative. Your corrected sentence is simplistic but does indeed fit the bill.
I, along with every other reader of this post, have no idea how many others did not understand what you were getting at despite knowing their own views on the matter. At the end of the day New Judge, your assertion was incorrect. That's it, pure and simple.