I recently listed to a nostr podcast and even people working in it said it would not be reasonable to recommend it for a secure messaging app at this point. Just because very early things like metadata leaking are not addressed yet. So not really an alternative.
I don't know what podcast you are mentioning or the context. Anyone can say anything on youtube.
We are talking about a transition from telegram, when comparing to that platform then NOSTR is undoubtely more secure when noticing that telegram doesn't even encrypt conversations by default and this isn't informed to users. Whereas in NOSTR you are made aware when a conversation is private between both parties.
Metadata is fetchable for 99% of messaging apps out there. If you'd ask me about making a more secure app then this involves continuous streaming of data, padding of messages to avoid content guessing and avoid the usage of internet as data channel.
So it really depends on what you consider secure and what it is compared against. Compared to Telegram it is more secure. Compared to a piece of paper encrypted with a custom algorithm and delivered by a trusted human transporter? Not really.
