The @daemon running on a local @node has to sync with other @remote-nodes. While it is not fully synced, @wallet may still be connected to the local node. Therefore, the @wallet cannot access the @blocks that are not yet synced on the local @node.
To allow the @wallet to be immediately usable, the daemon on the local @node uses a bootstrap node to which the RPC request are proxying to, giving access to the missing @blocks.
Note: the replies from the bootstrap node may be untrustworthy.