Now stock mkt wide valuation -
1. US equities are priced in USD
2. When USD is valued too strong against the other majors it would make US equities look cheap
3. Some speculators would short USD across majors with very small relative deposit. Then use the proceed to long the US equity mkt.
When volatility dies down, the trade will be profitable even if the equities stay at around the same price level.
If equities making $$, they win double.
Edit: Why it is bullish? Because the buying usually is done thru buy program.