My thoughts are that some on the spectrum will be as you describe, but many won’t. Some won’t even like words like “love” as they prefer emotions to be kept out of things. Others are more emotive and are able to express their feelings more freely, like yourself.
I have a very dear friend in the US who is expressive in telling me he loves me, and I can say “You are Loved” or “Love ya” back to him but we both know that this is a friendship kind of love. It’s nice to be able to express that, especially if you’ve been through alot together, and have supported each other for many years.
For those on the spectrum or not, anyone who has very clear boundaries, may never sign off with “Love You” or “Lots of Love” and it may feel very wrong for them to even mention “feelings of affection” in writing.
Those who’ve been burned or hurt badly in the past, may be especially cautious. People with PTSD for example, tend to keep people at a distance & can even find it hard to “expose themselves to relationships of any kind, remaining cautious throughout. There’ll be a tendency to self isolate, in spite of having “friends” in their lives.
What’s important if you do share a warm, close friendship with others, is clear communication … letting them know that in saying that you love them, that it’s purely said through friendship(if this is the case). If other feelings do develop, then that’s going to mean a whole other discussion that may or may not have a positive outcome for the friendship.