Problème de ARRAY sur mon calendrier

<?php 
namespace Calendar;

use PDO;

class Events {

    private $pdo;

    public function __construct(\PDO $pdo)
    {
        $this->pdo = $pdo;
    }

    /**
     * Récup les évenements entre deux dates
     * @param \DateTime $start
     * @param \DateTime $end
     * @return array
     */
    public function getEventsBetween(\DateTime $start, \DateTime $end): array{
        $sql = "SELECT * FROM events WHERE start BETWEEN '{$start->format('Y-m-d 00:00:00')}' AND '{$end->format('Y-m-d 23:59:59')}'" ;
        $statement = $this->pdo->query($sql);
        $results = $statement->fetchAll();
        return $results;
    }

    /**
     * Récup les évenements entre deux dates indexé par jour
     * @param \DateTime $start
     * @param \DateTime $end
     * @return array
     */
    public function getEventsBetweenByDay(\DateTime $start, \DateTime $end): array{
        $events = $this->getEventsBetween($start, $end);
        $days = [];
        foreach($events as $event){
            $date = explode(' ', $event['start'])[0];
            if(!isset($days[$date])){
                $days[$date] = [$event];
            }else{
                $days[$date][] = $event;
            }
        }
        return $days;
    }   
    
    /**
     * Récupére un évenement 
     * @param int $id
     * @return array
     * @throws \Exception
     */
    public function find (int $id): \Calendar\Event{ 
        require_once('Event.php');
        
        $statement = $this->pdo->query("SELECT * FROM events WHERE id = $id LIMIT 1");
        $statement->setFetchMode(\PDO::FETCH_CLASS, \Calendar\Event::class);
        $result = $statement->fetch();

        if($result === false){
            throw new \Exception('Aucun résultat a était trouvé');
        }
        $re = new \Calendar\Event($result['id'],$result['name'],$result['description'],$result['start'],$result['end']);
        return $re;
    }
}