This is the 11508th most frequent French word.
riant
Cheerful, smiling, or delightful.
Here, 'riant' is used as a present participle to describe an action (laughing) associated with the subject 'himself'.
Il m'a montré une photo de lui, riant aux éclats.
He showed me a photo of himself, laughing heartily.
In this usage, 'riant' is an adjective describing the landscape as cheerful or lively.
Nous avons admiré le paysage riant du sud de la France.
We admired the cheerful landscape of southern France.
Here, 'riant' is part of a gerund phrase ('en riant') conveying an action happening concurrently with the main verb ('managed').