Key:
When interpreting Sycamore’s theory, note the difference in translations:
OFFICIAL ENGLISH: "Let's talk about Mega Stones briefly." "My theory is that they're special stones irradiated by the light--the energy of the Legendary Pokémon YveltalY/XerneasX--fired from the ultimate weapon 3,000 years ago." "And that's what I think they are." "It's even possible that stones like Fire Stones were what turned into these Mega Stones." https://bulbapedia.bulbagarden.net/wiki/Professor_Sycamore/Quotes
JAPANESE: 「そもそも メガストーンとは なんだろう？ これは ボクの 推測だけど 3000年前 撃ちだされた 最終兵器の 光…… 伝説ポケモン ゼルネアスX/イベルタルYの パワーを 浴びた 特殊な 石 それが メガストーンだと おもう もしかしたら ほのおのいし などが 変化したのかも しれないね…… https://wiki.ポケモン.com/wiki/プラターヌ博士/引用
ENGLISH TRANS. DeepL: What is the Megastone anyway? This is my guess, but I think it's a special stone that was hit by the power of the ultimate weapon shot 3,000 years ago, the light ...... legendary Pokémon Xerneas /Yveltal. I think it's a megastone. Maybe it's a change from a Fire Stone, or something....… https://www.deepl.com/en/translator#ja/en/しれないね……
ENGLISH TRANS. RomajiDesu: "In the first place, what is a Mega Stone? This is just my guess, but it's a special stone that was immersed in the power of the final weapon that was fired 3,000 years ago... the legendary Pokémon Xerneas X/Yveltal Y. It's a Mega Stone. I think it might be that things like firestones have changed… https://www.romajidesu.com/translator
Using some cross-language linguistic analysis we can discern a better understanding of Sycamore’s theory.
The しれないね…… [shirenai ne] at the end of Sycamore’s original Japanese statement denotes a ‘maybe’ OR a ‘who knows, right?’ . Shirenai, a compound word consisting of ‘shieru’ - meaning ‘was knowing’ - and ‘nai’ - which is basically a negative modifier for verbs. When combined, ‘shirenai’ usually means uncertain but possible. https://aclanthology.org/Y98-1007.pdf
‘ne’ is a particle when that used at the end of a sentence is generally the speaker asking for a concurrence from the listener. This often translates to the English phrase “right?”.
For example, [今日 は 土曜日 です ね, Kyou wa doyoubi desu ne.] would translate to: “Today is Saturday, right?.” Bussu
This analysis suggests that the initial intention the writers had for Sycamore’s theory was for him to display a lower level of confidence in his postulation than what the official English translation presentes.