According to our documentation, the getPermissions() and getPermissionsForUser() methods can return up to four values:

• view
• modify
• comment
• admin

Internally, the "modify" value is returned if the user has EDIT permission on the space, which is only true if the user is a space admin. What we should check is whether the user has CREATEEDIT_PAGE_PERMISSION on the space, which will be a much more sensible "modify" permission.