Voadam
Legend
From the Monster Manual (1977) intelligence of dragons:
Black: Average
Blue: Very
Brass: High
Bronze: Exceptional
Copper: High
Gold: Genius
Green: Average-Very
Red: Exceptional
Silver: Exceptional
White: Average
None are beasts (in terms of intelligence), and all dragons are at least human intelligence (average) and most are more intelligent than that.
You missed a bit on the low end white dragons there.
The entry for white dragons is actually: "INTELLIGENCE: Average (low)" Average is only 8-10 so low end of that would be 8. Low intelligence is 5-7 range.
MM 1e page 6 said:0 Non-intelligent or not ratable
1 Animal intelligence
2-4 Semi-intelligent
5-7 Low intelligence
8-10 Average (human) intelligence
13-14 Highly intelligent
15-16 Exceptionally intelligent
17-18 Genius
19-20 Supra-genius
21+ Godlike intelligence
11-12 Very intelligent
In Moldvay Basic it called dragons intelligent but 90% to 50% of non-gold dragons could not talk at all (even in the Dragon language) and were just big intelligent flying predators with breath weapons.
Moldvay Basic page B34 said:TALKING: Dragons are intelligent, and some dragons can speak Dragon and Common. The percentage listed under Chance of Talking is the chance that a dragon will be able to talk.
Seeing most dragons as intelligent hissing and spitting dangerous beasts is not out of line with a Basic D&D background.