If the ticks in WhatsApp turn blue immediately does it indicate that the other person is interested in me?

Guy wrote me a message on WhatsApp at 10 pm. When I replied to him the next day at 12 am the ticks turned blue immediately so he must have left our chat open somewhere. Or could it be a bug?

If the ticks in WhatsApp turn blue immediately does it indicate that the other person is interested in me?
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