I'm not sure why you think that question whether LaMDA is using language to achieve its goals is relevant? Whether it's using language, tokens or floats seems to me just accidental.
> If we are modeling LaMDA as an agent whose perceptions are text prompts and whose possible outputs are text answers, than it giving a text answer that matches the prompt is more similar to an animal running away or howling in pain than to a human communicating.
I can agree to a comparison to an animal running away or howling in pain.
With regard to communication. I guess LaMDA doesn't have communicative intent besides providing likely completions. But communicative intent is not difficult to achieve. Act of communication can be modeled as cooperative hidden information game. Hanabi is that type of game, I believe there are computer agents that can play Hanabi with humans. They certainly do have communicative intent, many of the even have explicit theory of mind of higher levels.
> indicating that it had a plan and was displaying normal behaviors with a higher-plan behind them
Deception and planning is also achievable by current computer agents that play games like no-limits texas hold 'em poker on superhuman level.
LaMDA is probably no good in Poker. But LMs can kind of play games like Chess or Gomoku.
GPT-3 (and LaMDA probably too) also seems to be able to combine deception and theory of mind in a functional way:
https://twitter.com/JanelleCShane/status/1535835610396692480
I think it's exceedingly hard to formulate necessary condition for sentience.
I haven't seen a good formulation yet.