Most definitely! Bitcoin is a the most singular coin that all the coin including tokens are priced against. Therefore, if anything happen to bitcoin prices it is easily felt by cryptocurrency ecosystem in general!
Yes they are directly impacted with fluctuations of bitcoin prices. But to elaborate more, when bitcoin price decreases, many altcoin asset holders would trade their coins for bitcoin, since its price is dropping and they will view it as a perfect time to invest.
Given the volume out of an alt, its market price will then decrease as a consequence.
Though that is but one of the reasons, but the most logical explanation.
On another note, don't confuse ICOs as alts. ICOs are yet to enter the market and therefore cannot be referred to as altcoin or a coin.
Anyway, I believe same principle applies as what you have explained. When investors invest in ICOs, then dip comes in, most of these investors may trade their assets for bitcoin, and affect prices in turn.
So yes, it can affect ICOs.