You are correct that the reader completes some abbreviated sentences themselves, but they only do so from context. For example, I would expect a sentence like "many doctors average 70 hours a week" to be part of a wider conversation about the number of hours worked.
Your statement seems wrong, but not for grammatical reasons. It seems wrong for mathematical and logical reasons:
The expenditure for education was highest in India, at 15%, followed by 13% in Thailand. Meanwhile, the remaining countries averaged around 7%.
The previous percentages were not expressed as averages (unless your wider context has said that they are?) It makes no sense to compare actual percentages for some countries against an average of several others. If you're trying to make the point that 7% for the 'remaining countries' in your data is markedly lower than India's 15% and Thailand's 13% that could be extremely misleading because a country with a very high rate such as 20% and another with 1% could result in a low average if you lumped them together, and any good data analyst would wonder why you are not making a straight comparison.
You clarified in comment that the figures for India and Thailand are actual figures (not 'averages' as such, although no doubt they represent spending in a specific time period such as a financial year) and that you don't want to detail all the other countries' figures. In that case, don't use the word 'average' at all. An average is the ratio of summation of all the data to the number of units present in the list, but as a general rule, you should not average out a set of percentages because the denominators in each are not equal, ie those countries are not of equal size. For example, consider if a set of 100 people where 1 person meets the metric criteria (1%) was added to a set of just 1 person that met the criteria (100%) - the percentages would average at around 50%, yet only 2 persons out 101 met the criteria. That's clearly not what you're doing - you're just trying to say that all the percentages, viewed individually, were around the 7% mark.
You should probably make a broader statement like:
Education expenditure was highest in India, at 15%, followed by 13% in Thailand. The remaining countries had expenditures of around 7%.