"Bearish" and "bullish" are terms from finance; bearish means you're pessimistic, bullish is optimistic.

https://en.wikipedia.org/wiki/Bull_(stock_market_speculator)

https://en.wikipedia.org/wiki/Market_trend#Bear_market

It's stock market slang:

- bullish - "bull market" - a positive outlook

- bearish - "bear market" - a negative outlook

So being "bearish" means he's skeptical about that being the case

Bearish = pessimistic (in finance, thinking stock will go down), the opposite of bullish = optimistic (thinking stock will go up)